This nonprovisional application claims priority under 35 U.S.C. § 119(a) on patent application Ser. No. 2001-314221 filed in JAPAN on Oct. 11, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a-golf club shaft and more particularly to a lightweight golf club shaft, made of a fiber reinforced resin, which has an improved vibration-damping performance.
2. Description of the Related Art
In recent years, a golf club shaft composed of a reinforcing fiber such as a carbon fiber having a high strength and a high rigidity is manufactured and commercially available. As the strength and the rigidity of the carbon fiber increase, a lightweight golf club shaft can be manufactured.
As the golf club shaft becomes more lightweight, a head speed of the golf club will increase when the club is swung. Thus, the player can hit a golf ball a longer distance with this golf club. On the other hand, as the golf club shaft becomes more lightweight, the player feels unpleasant vibrations and impacts that are generated when the player hits the golf ball with the golf club. As the golf club shaft becomes more lightweight, the frequency of the vibration thereof becomes higher than the conventional golf club shaft. Therefore in recent years, players are increasingly damaged at their elbows and shoulders by vibrations and impacts generated when they hit the golf ball with golf clubs composed of the lightweight golf club shafts.
To suppress the vibrations generated when the player hits the golf ball many proposals are made. For example, in Japanese Patent Application Laid-Open Nos.9-216958 and 10-36638, resinous particles of an ethylene copolymer and rubber particles are mixed with the resin of the fiber reinforced resin layer to form a prepreg and an epoxy resinous composition using the fiber reinforced resin superior in vibration suppression performance and resistance to impacts.
In the golf club shaft having the three-layer construction disclosed in Japanese Patent Application Laid-Open No.5-123428, to obtain vibration absorption performance and a soft feeling, the vibration suppression material layer is inserted into the layer of vibration suppression materials.
In the prepreg disclosed in Japanese Patent Application Laid-Open Nos.9-216958 and 10-36638, the prepreg itself has vibration suppression performance. However, in the case where the golf club shaft is composed of the prepeg, the prepreg is incapable of achieving dramatic vibration-damping performance to such an extent that the player can feel.
In the golf club shaft disclosed in Japanese Patent Application Laid-Open No.5-123428, it is difficult to design the golf club shaft in such a way as to flex it. Since the degree of freedom in designing the golf club is low, it is difficult make it lightweight and increase the flight distance of the golf ball while allowing the golf club shaft to have vibration-damping performance. Further it is difficult to mold the material for the golf club shaft. Thus, the golf club shaft has a problem that there is a large lot-to-lot variation in its vibration suppression function.